Ammonite

Ammonites are mollusks in a coiled shell. They are some of the most recognizable fossils.

Actual ammonite fossils are relatively uncommon, believe it or not, because what are usually found are the internal molds. You can tell the difference between the two by looking for suture lines, which are squiggly lines in different patterns, depending on the species. Only internal molds preserve the suture lines.